2. Description of Prior Art
None of the prior art fins provide methods for maximizing the storage of energy during use or maximizing the release of such stored energy in a manner that produces significant improvements in efficiency, speed, and performance.
No prior fin designs employ adequate or effective methods for reducing the blade's angle of attack around a transverse axis sufficiently enough to reduce drag and create lift in a significantly consistent manner on both relatively light and relatively hard kicking strokes.
Prior art beliefs, convictions, and design principles teach that highly flexible blades are not effective for producing high swimming speeds. Such prior principles teach that high flexibility wastes energy since it permits kicking energy to be wasted in deforming the blade rather than pushing water backward to propel the swimmer forward. A worldwide industry convention among fin designers, manufactures, retailers and end users is that the more flexible the blade, the less able it is to produce power and high speed. The industry also believes that the stiffer the blade, the less energy is wasted deforming on the blade and the more effective the fin is at producing high speeds. The reason the entire industry believes this to be true is that no effective methods have existed for designing blades and load bearing ribs that exhibit large levels of blade deflection around a transverse axis in a manner that is capable of producing ultra-high swimming speeds. Prior fin design principles also teach that the greater the degree of blade deflection around a transverse axis on each opposing kicking stroke, the greater the degree of lost motion that occurs at the inversion point of each stroke where the blade pivots loosely from the high angle of deflection on one stroke, through the blade's neutral position, and finally to the high angle of deflection on the opposite stroke. Prior principles teach that lost motion wastes kicking energy throughout a significantly wide range of each stroke because kicking energy is expended on reversing the angle of the blade rather that pushing water backward. Also, prior swim fin design principles teach that the greater the degree of flexibility and range of blade deflection, the greater the degree of lost motion and the larger the portion of each kicking stroke that is wasted on deflecting the blade and the smaller the portion of the stroke that is used for creating propulsion. Furthermore, prior principles teach that such highly deflectable blades are vulnerable to over deflection during hard kicks when high swimming speeds are required. Although it is commonly known that highly deflectable blades create lower strain and are easier to use at slow speeds, such highly deflectable blades are considered to be undesirable and unmarketable since prior versions have proven to not work well when high swimming speeds are required.
Because prior fins are made significantly stiff to reduce lost motion between strokes as well as to reduce excessive blade deflection during hard kicks, prior fins place the blade at excessively high angles of attack during use. This prevents water from flowing smoothly around the low-pressure surface or lee surface of the blade and creates high levels of turbulence. This turbulence creates stall conditions that prevent the blade from generating lift and also create high levels of drag.
Since the blade remains at a high angle of attack that places the blade at a significantly horizontal orientation while the direction of kicking occurs in a vertical direction, most of the swimmer's kicking energy is wasted pushing water upward and downward rather that pushing water backward to create forward propulsion. When prior fins are made flexible enough to bend sufficiently around a transverse axis to reach an orientation capable of pushing water in a significantly backward direction, the lack of bending resistance that enables the blade to deflect this amount also prevents the blade from exerting a significant backward force upon the water and therefore propulsion is poor. This lack of bending resistance also subjects the blade to high levels of lost motion and enables the blade to deflect to an excessively low angle of attack during a hard kick that is incapable of producing significant lift. In addition, prior fin design methods that could permit such high deflections to occur do not permit significant energy to be stored in the fin during use and the fin does not snap back with significant energy during use. Again, a major dilemma occurs with prior fin designs: poor performance occurs when the fin is too flexible as well as when it is too stiff.
One of the major disadvantages that plague prior fin designs is excessive drag. This causes painful muscle fatigue and cramps within the swimmer's feet, ankles, and legs. In the popular sports of snorkeling and SCUBA diving, this problem severely reduces stamina, potential swimming distances, and the ability to swim against strong currents. Leg cramps often occur suddenly and can become so painful that the swimmer is unable to kick, thereby rendering the swimmer immobile in the water. Even when leg cramps are not occurring, the energy used to combat high levels of drag accelerates air consumption and reduces overall dive time for SCUBA divers. In addition, higher levels of exertion have been shown to increase the risk of attaining decompression sickness for SCUBA divers. Excessive drag also increases the difficulty of kicking the swim fins in a fast manner to quickly accelerate away from a dangerous situation. Attempts to do so, place excessive levels of strain upon the ankles and legs, while only a small increase in speed is accomplished. This level of exertion is difficult to maintain for more than a short distance. For these reasons scuba divers use slow and long kicking stokes while using conventional scuba fins. This slow kicking motion combines with low levels of propulsion to create significantly slow forward progress.
Prior art fin designs do not employ efficient and methods for enabling the blade to bend around a transverse axis to sufficiently reduced angles of attack that are capable of generating lift while also providing efficient and effective methods for enabling such reduced angles of attack to occur consistently on both light and hard kicking strokes.
Prior art fins often allow the blade to flex or bend around a transverse axis so that the blade's angle of attack is reduced under the exertion of water pressure. Although prior art blades are somewhat flexible, they are usually made relatively stiff so that the blade has sufficient bending resistance to enable the swimmer to push against the water without excessively deflecting the blade. If the blade bends too far, then the kicking energy is wasted on deforming the blade since the force of water applied to the blade is not transferred efficiently back to the swimmers foot to create forward movement. This is a problem if the swimmer requires high speed to escape a dangerous situation, swim against a strong current, or to rescue another swimmer. If the blade bends too far on a hard kick, the swimmer will have difficulty achieving high speeds. For this reason, prior fins are made sufficiently stiff to not bend to an excessively low angle of attack during hard and strong kicking stokes.
Because prior fin blades are made stiff enough so that they do not bend excessively under the force of water created during a hard kick, they are too stiff to bend to a sufficiently reduced angle of attack during a relatively light stroke used for relaxed cruising speeds. If a swim fin blade is made flexible enough to deflect to a sufficiently reduced angle of attack during a light kick, it will over deflect under the significantly higher force of water pressure during a hard kick. Prior fins have been plagued with this dilemma. As a result, prior fins are either too stiff during slower cruise speeds in order to permit effectiveness at higher speeds, or fins they are flexible and easy to use at slow speeds but lack the ability to hold up under the increased stress of high speeds. This is a major problem since the goal of scuba diving is mainly to swim slowly in order to relax, conserve energy, reduce exertion, and conserve air usage. Because of this, prior fins that are stiff enough to not over deflect during high speeds will create muscle strain, high exertion, discomfort, and increased air consumption during the majority of the time spent at slow speeds.
Because prior art fins attempt to use significantly rigid materials within load bearing ribs and blades to prevent over deflection, the natural resonant frequency of these load bearing members is significantly too high to substantially match the kicking frequency of the swimmer. None of the prior art discloses that such a relationship is desirable, that potential benefits are known, or that a method exists for accomplishing this in an efficient manner that significantly improves performance. Furthermore, soft and highly extensible materials are not used to provide load bearing structure and instead, only highly rigid materials are used that have elongation ranges that are typically less than 5% during even the hardest kicking strokes.
Some prior designs attempt to achieve consistent large scale blade deflections by connecting a transversely pivoting blade to a wire frame that extends in front of the foot pocket and using either a yieldable or non-yeildable chord that connects the leading edge of the blade to the foot pocket to limit the blade angle. This approach requires the use of many parts that increase difficulty and cost of manufacturing. The greater the number of moving parts, the greater the chance for breakage and wear. Many of these designs use metal parts that are vulnerable to corrosion and also add undesirable weight. Variations of this approach are seen in U.S. Pat. Nos. 3,665,535 (1972) and 4,934,971 (1988) to Picken, and U.S. Pat. Nos. 4,657,515 (1978), and 4,869,696 (1989) to Ciccotelli. U.S. Pat. No. 4,934,971 (1988) to Picken shows a fin which uses a blade that pivots around a transverse axis in order to achieve a decreased angle of attack on each stroke. Because the distance between the pivoting axis and the trailing edge is significantly large, the trailing edge sweeps up and down over a considerable distance between strokes until it switches over to its new position. During this movement, lost motion occurs since little of the swimmer's kicking motion is permitted to assist with propulsion. The greater the reduction in the angle of attack occurring on each stroke, the greater this problem becomes. If the blade is allowed to pivot to a low enough angle of attack to prevent the blade from stalling, high levels of lost motion render the blade highly inefficient. This design was briefly brought to market and received poor response from the market as well as ScubaLab, an independent dive equipment evaluation organization that conducts evaluations for Rodale's Scuba Diving magazine. Evaluators stated that the fin performed poorly on many kick styles and was difficult to use while swimming on the surface. The divers reported that they had to kick harder with these fins to get moving in comparison to other fin designs. The fins created high levels of leg strain and were disliked by evaluators. A major problem with this design approach is that swimmers disliked the clicking sensation created by of the blade as it reached its limits at the end of each fin stroke.
Prior fin designs using longitudinal load bearing ribs for controlling blade deflections around a transverse axis do not employ adequate methods for reducing the blade's angle of attack sufficiently enough to reduce drag and create lift in a significantly consistent manner on both relatively light and relatively hard kicking strokes. Many prior art fins use substantially longitudinal load bearing support ribs to control the degree to which the blade is able to bend around a transverse axis. These ribs typically connect the foot pocket to the blade portion and extend along a significant length of the blade. The ribs usually extend vertically above the upper surface of the blade and/or below the lower surface of the blade and taper from the foot pocket toward the trailing edge of the blade. Hooke's Law states that strain, or deflection, is proportional to stress, or load placed on the rib. Therefore the deflection of a flexible rib the load varies in proportion to the load placed on it. A light kick produces a minimal blade deflection, a moderate kick produces a moderate blade deflection, and a hard kick produces a maximum blade deflection. Because of this, prior art design methods for designing load supporting ribs do produce significantly consistent large-scale blade deflections from light to hard kicks.
Prior fin designs using longitudinal load bearing ribs for controlling blade deflections around a transverse axis do not employ adequate methods for reducing the blade's angle of attack sufficiently enough to reduce drag and create lift in a significantly consistent manner on both relatively light and relatively hard kicking strokes.
These ribs are designed to control the blade's degree of bending around a transverse axis during use. Because of the need for the blade to not over deflect during hard kicking strokes, the ribs used in prior fin designs are made relatively rigid. This prevents the blade from deflecting sufficiently during a light kick. This is because the rib acts like a spring that deflects in proportion to the load on it. Higher loads produce larger deflections while lower loads produce smaller deflections. Because prior fins cannot achieve both of these performance criteria simultaneously, prior designs provide stiff ribs to permit hard kicks to be used. The ribs often use relatively rigid thermoplastics such as EVA (ethylene vinyl acetate) and fiber reinforced thermoplastics that have short elongation ranges that are typically less than 5% under very high strain and high loading conditions, and these materials typically have insignificantly small compression ranges. When rubber ribs are used, harder rubbers having large cross sections are used to provide stiff blades that under deflect during light kicking strokes so that they do not over deflect during hard kicking strokes.
Even if more flexible materials are substituted in the ribs to enable the blade to deflect more under a hard kick, no prior art method discloses how to efficiently prevent the blade from over deflecting on a hard kick.
The vertical height of prior stiffening ribs often have increased taper near the trailing edge of the blade to permit the tip of the blade to deflect more during use. Flexibility is achieved by reducing the vertical height of the rib since this lowers the strain on the material and therefore reduces bending resistance. Again, no method is used to provide consistent deflections across widely varying loads. The approach of reducing the vertical height of a rib to increase flexibility is not efficient since it causes this portion of the rib to be more susceptible to over deflection and also reduces performance by minimizing energy storage within the rib. U.S. Pat. No. 4,895,537 (1990) to Ciccotelli reduces the vertical height of a narrow portion on each of two longitudinal support beams to focus flexing in this region. This makes the ribs more susceptible to over deflection and minimizes energy storage.
Another problem is that prior fin design methods teach that in order to create a high powered snapback effect the ribs must attain efficient spring characteristics by using materials that have good flexibility and memory but have relatively low ranges of elongation. Elongation is considered to be a source of energy loss while highly inextensible thermoplastics such as EVA and hi-tech composites containing materials such as graphite and fiberglass are considered to be state of the art for creating snap back qualities. These materials do not provide proper performance because they provide substantially linear spring deflection characteristics that cause the blade to either under deflect on a light kick or over deflect on a hard kick. Furthermore, these materials require that a small vertical thickness be used in order for significant bending to occur during use. This greatly reduces energy storage and reduces the power of the desired snap back.
The highly vertical and narrow cross-sectional shape of prior ribs makes them highly unstable and vulnerable to twisting during use. When the vertical rib is deflected downward, tension is created on the upper portion of the rib as well as compression on the lower portion of the rib. Because the material on the compression side must go somewhere, the lower portion of the rib tends to bow outward and buckle. This phenomenon can be quickly observed by holding a piece of paper on edge as a vertical beam and applying a downward bending force to either end of the paper. Even if the paper is used to carry a force over a small span, it will buckle sideways and collapse. This is because the rib's resistance to bending is greater than its resistance to sideways buckling. If more resilient materials are used in prior art rails, then the rails will buckle sideways and collapse. This causes the blade to over deflect.
Some prior art ribs have cross-sectional shapes that are less vulnerable to collapsing, however, none of these prior art examples teach how to create similar large-scale blade deflections on both light and hard kicking strokes.
U.S. Pat. No. 5,746,631 to McCarthy shows load bearing ribs that have a rounded cross-section, no methods are disclosed that permit such rails to store increased levels of energy or experience substantially consistent blade deflections on both light and hard kicking strokes. Although it is stated that alternate embodiments may permit the lengthwise rails to pivot around a lengthwise axis where the rails join the foot pocket so that the rails can flex near the foot pocket, no method is identified for creating consistent deflections on light and hard kicks using material elongation and compression.
U.S. Pat. No. 4,689,029 (1987) to Ciccotelli shows two flexible longitudinal ribs extending from the foot pocket to a blade spaced from the foot pocket. Although Ciccotelli states that these ribs have elliptical cross-sections to prevent twisting, he also states that these flexible ribs are made sufficiently rigid enough to no over deflect on hard kicks. The patent states that the “flexible beams are made of flexible plastic and graphite or glass fibers may be added to increase the stiffness and strength. The flexible beams have to be stiff enough to prevent excessive deflection of the blade on a hard kick by the swimmer otherwise a loss of thrust will result.” This shows that he believes that stiffer ribs are required to provide maximum speed. This also shows that Ciccotelli believes that the use of softer and highly extensible materials in the ribs will cause over deflection to occur during hard kicks and therefore unsuitable for use when high swimming speeds are needed. FIG. 2 shows that the range of deflection (17) is quite small and does not produce a sufficiently large enough reduction in the angle of attack to create proper lift and to prevent stall conditions. This shows that Ciccotelli is not aware of the value of larger blade deflections. This limited range of deflection shows that the flexible beams he uses are only slightly flexible and relatively rigid. In addition to providing insufficient deflection, no method is given for creating such deflections in a consistent manner on both light and hard kicks. Ciccotelli also states that the elliptical cross-section of the beams near the foot pocket is approximately 1.500 by 0.640, and that a larger cross section would be required for stiffer models. The cross-sectional measurements are at a height to width ratio of approximately 3 to 1. If this ratio were used with soft and highly extensible materials, the ribs would buckle sideways and collapse during use. Also, the top view in FIG. 1 shows that the ribs bend around a slight corner before connecting to the wire frame. This corner creates high levels of instability within the rib and makes the rib even more vulnerable to buckling, especially when more extensible materials are used. No adequate methods or structure are disclosed that describe how to avoid buckling on softer materials or how to obtain consistent large-scale deflections on both light and hard kicks. No methods are disclosed for storing large sums of energy within the ribs and then releasing such energy during use.
U.S. Pat. No. 4,773,885 (1988) to Ciccotelli is a continuation-in-part of U.S. Pat. No. 4,689,029 (Ser. No. 842,282) to Ciccotelli that is described above. U.S. Pat. No. 4,689,029 displays that Ciccotelli still does not disclose a method for creating large scale blade deflections on light kicks while simultaneously preventing over deflection on hard kicks. Although U.S. Pat. No. 4,773,885 describes flexible beams that are made of a rubber-like thermoplastic elastomer, the purpose of these flexible beams are to enable to beams to flex sufficiently enough to enable a diver to walk across land or through heavy surf. No method is disclosed to for designing such beams to create consistent large-scale blade deflections on varying loads. No mention is made of any attempts to create large-scale blade deflections on light kicks. The only benefit listed to having flexible beams is to enable the diver to walk across land while carrying equipment. No mention is made of methods for creating and controlling specific blade deflections and no mention is made for optimizing the storage of energy. This shows that Ciccotelli is not aware that such benefits are possible and is not aware of any methods or processes for creating and optimizing such benefits. Furthermore, Ciccotelli states in column 3 lines 20 through 37 that “The beams 2 are sufficiently flexible to bend enough so that the wearer, with his foot in the pocket 1 can walk along a beach in a normal fashion, with his heel raising as his foot rolls forward on its ball. Nevertheless, beams 2 are sufficiently stiff that during swimming, the flexible beams 2 flex only enough to provide good finning action of the blade 4, in accordance with the principles described in the above-referenced application Ser. No. 842,282.” He states that the beams must be stiff in accordance with the principles of Ser. No. 842,282 (U.S. Pat. No. 4,689,029) which only shows a substantially small range of blade deflection (17) in FIG. 2 of the drawings. U.S. Pat. No. 4,773,885 shows no desired range of blade deflection in the drawings and specifically states that during swimming the beams act in accordance with what is now U.S. Pat. No. 4,689,029 which shows in FIG. 2 the small range of flexibility Ciccotelli believes is ideal. This range is too small since it does not permit the blade to reach a sufficiently reduced angle of attack to efficiently create lift and reduce stall conditions. Because he states that the beams should be stiff enough to not over deflect during a hard kick and only shows a small range of deflection (17) in FIG. 2. It is evident that Ciccotelli believes that deflections in excess of range 17 in FIG. 2 is an “excessive deflection” that will cause a “loss of thrust”. He discloses no other information to specify what he believes to be an excessive angle of deflection. This shows that shows that Ciccotelli does not intend his flexible beams to be used in a manner that enables the blade to experience significantly high levels of deflection. This also shows that Ciccotelli is unaware of any benefits of large-scale blade deflections and is unaware of methods for designing ribs in a manner that create new benefits or new unexpected results from large-scale blade deflections.
Another problem with U.S. Pat. No. 4,773,885 is that the cross sectional shape of the rail creates vulnerability to twisting and buckling. Ciccotelli admits that the beams tend to buckle and twist when the blade deflects while walking on land. If the beams buckle and twist under the larger deflections occurring while walking, the beams will also buckle and twist if the beams are made with sufficiently flexible enough grades of elastomeric materials to exhibit high levels of blade deflections during use. The reason the rails are vulnerable to buckling is that the first stages of twisting causes the rectangular cross-section to turn to a tilted diamond shape relative to the direction of bending. The upper and lower corners of this portion of the beam are off center from the beam axis (the axis passing through the cross-sectional geometric center of the beam) of the beam during bending. These corners also extend higher above and below the beam axis relative to bending than the upper and lower surfaces of the rectangular cross section that existed before twisting. Because stresses are greatest at the highest points above and below the beam's neutral surface (a horizontal plane within the beam relative to vertical bending, in which zero bending stress exists), these tilted corners have the highest levels of strain in the form of tension and compression. Because these corners and the high strain within them are oriented off center from the beam axis, a twisting moment is formed which cause the beams to buckle prematurely while bending. As the beam twists along its length, bending resistance and twisting moments vary along the length of the beam. This causes the beams to bend unevenly and forces energy to be lost in twisting the beam rather than creating propulsion. Although Ciccotelli provides extra width at the lower end of the beam to reduce the bulking there under compression, he states that this is done to reduce buckling if the blade jams into the ground while walking. He does not state that he this is done to create any benefits while swimming. He does not use cross sectional thickness to create new and unobvious benefits while swimming. Because he desires small ranges of blade deflection, he does not disclose a method for using cross-sectional shape in a manner that enables high levels of deflection to occur on light kicks while preventing excessive deflection on hard kicks. He also does not disclose any methods for using cross-sectional shapes to provide increased energy storage.
None of the prior art discloses methods for designing longitudinal load bearing ribs that are able to permit the blade to reach high levels of provide specific minimum and maximum reduced angles of attack around a transverse axis that are desired at slow swimming speeds and maximum reduced angles of attack that are desired at high swimming speeds along with an efficient and effective method for achieving these minimum and maximum angles regardless of swimming speeds.
U.S. Pat. No. 3,411,165 to Murdoch (1966) displays a fin which uses a narrow stiffening member that is located along each side of the blade, and a third stiffening member that is located along the central axis of the blade. Although oval shaped ribs are shown, the use of metal rods within the core of these ribs prevents bending from occurring
U.S. Pat. No. 4,541,810 to Wenzel (1985) employs load supporting ribs that have a cross-section that is wide in its transverse dimension and thin in its vertical dimension. The rib is intended to twist during use. The thin vertical height of the rib prevents efficient energy storage and no methods are disclosed for creating consistent large-scale blade deflections with the ribs.
U.S. Pat. No. 4,857,024 to Evans (1989) shows a fin that has a relatively thin flexible blade and uses no load bearing ribs. The center portion of the blade is made thicker to create increased bending resistance along the center. The drawings show that during use the stiffer central portion of the blade arches back around a transverse axis to an excessively reduced angle of attack where the blade then slashes back at the end of the stroke in a snapping motion to propel the swimmer forward. The blade deflects to an excessively low angle of attack to efficiently generate lift. The thin blade offers poor energy storage and snap back energy is low. Underwater tests conducted by ScubaLab, an independent dive equipment evaluation organization, utilized men and women divers wearing full scuba gear that swam numerous test runs over a measured 300-foot open ocean course. These tests found that this design consistently produced the lowest top end speeds of any production fins tested. No methods are disclosed for creating consistent large-scale deflections under varying loads or for creating increased energy storage.
Although the specification and drawings mention the formation of a snap back motion, no S-shaped substantially longitudinal sinusoidal waves are displayed in the drawings or described in the specification. Although the blade has a thicker central portion, this thicker portion is significantly too thin to permit the use of substantially soft materials that have significantly high elongation and compression rates since such flexibility would cause the blade to deflect excessively. As a result, this design is forced to use stiffer materials having significantly lower elongation and compression ranges under the loads created during kicking strokes. These types of materials support a natural resonant frequency that is significantly higher than the kicking frequency of a swimmer's strokes. No mention is made to suggest that such a condition is anticipated or desired. Although the tip regions are designed to flex relative to the thicker blade portion along the fin's center axis, the drawings and specification do not disclose a method for simultaneously creating a standing wave or opposing sinusoidal oscillation phases in an S-shaped manner along the length of the blade in general or along the length of the more flexible side regions of the blade.
U.S. Pat. No. 2,423,571 to Wilen (1944) shows a fin that has a stiffening member along the central axis of the blade that has a thin and highly flexible membrane extending to either side of the central stiffening member. The thin and flexible membrane is shown to undulate during use and have multitudes of opposing oscillation phases along the length of the blade's side edges, in which a sinusoidal wave has adjacent peaks and troughs displayed by convex up and convex down ripples. Numerous and multiple oscillations existing simultaneously along the length of the fin would require a user to employ a ultra-high kicking frequency that would be unnatural. Such ultra high frequency oscillations would also be inefficient since the back and forth movement of the blade would have to be minimized and this would minimize water displacement and therefore propulsion. Also, only thin materials are used, thus high levels of elongation and compression do not occur during bending and are not required to create blade deflections. No such methods are disclosed to increase energy storage. The central stiffening member, or load bearing member does not have opposing oscillation phases and therefore Wilen does not anticipate the need for this to occur. Wilen discloses no methods for permitting this to occur in a manner that prevents the member from over deflecting during a hard kicking stroke. Although it is mentioned that a more flexible material may be used at the base of the central stiffening member to provide limited movement and pivoting near the foot pocket, no effective method is disclosed for permitting this more flexible material to allow significantly large scale blade deflections to occur during a light kick while preventing over deflection during a hard kick.
The thin membrane used in this fin is far too thin to effectively propagate a lengthwise wave having opposing phases of oscillation since the dampening effect of the surrounding water quickly dissipates the small amount of wave energy stored in this thin material. Instead of creating propulsion, the thin blade will flop loosely without having enough bending resistance to accelerate water. Rather than moving water, the thin membrane will over deflect and stay substantially motionless while the foot and stiffening member move up and down. Even though it is mentioned that stiffening members can be used to reinforce the side portions of the blade no method is disclosed for effectively preventing these portions from over deflecting during hard kicking strokes while also permitting large scale blade deflections to occur during light kicking strokes. No methods are disclosed that permit significantly increased energy to be stored and then released in the blade. Because such methods are not used or disclosed, this fin does not produce significant propulsion and is not usable.
From both the top view and the side view of FIG. 15 and FIG. 16, it can be seen that Wilen's fin creating a longitudinal wave that has many peaks and troughs across the length of the blade. This means that the frequency of the propagated wave is significantly higher than the frequency of kicking strokes. Wilen does not disclose methods for correlating blade undulation frequency, wavelength, amplitude, and period with the swimming stroke that creates new levels of performance and unexpected results.
Some prior art free diving fins use very long blades that are often 2 to 4 feet long. Although soft rubber rails are often used along the outer side edges of these fins, they are not load bearing structures since the majority of the load is placed on the central rigid blade that is often bolted in a rigid manner to the sole of the foot pocket. The central rigid blade is the load bearing structure and it is made out of a very thin and highly inextensible material such as fiberglass or carbon reinforced resin or thermoplastic. These materials often have hardness readings that far exceed the Shore A hardness scale and progress in to the much harder Shore D hardness scale. These materials have elongation limits that are less than 3% compression limits that are less than 1%, even under the hardest kicking strokes. To permit bending, these load-bearing structures are given very small vertical dimensions or thickness to permit bending about a transverse axis without significant elongation or compression being required to experience such bending. This thin vertical dimension cause the height above the blade's neutral bending axis to be very low and this causes bending resistance to occur at a extremely small lever arm which reduces snap back efficiency of the blade under the damping effect of the surrounding water. In addition, the small lever arm combines with negligible elongation and compression rates to prevent efficient storage of energy within the blade during use. Although such very long and thin free diving blades can be observed taking on a sinusoidal form during use, the lack of a significant lever arm and adequate elongation rates and compression rates prevent such blades from performing efficiently under the damping effect of water. Also, such long blades are excessively large and cumbersome to many divers both during use and while being packed for traveling. Furthermore, these long blades require a large range of leg motion that causes increased oxygen usage since the large hip, thigh, and quadriceps muscles must be used to drive these large fins.
The thin blade thickness and small lever arm create linear blade deflections, which either under deflect during a light kick or over deflect during a heavy kick. These many problems cause a long, thin, rigid, and inextensible load-bearing blade to be an undesirable solution.
Non of the prior art fin designs teach effective methods for tailoring and adjusting the natural resonant frequency of a blade to create new results and new levels of efficiency. None of the prior art teaches how to use significantly soft and extensible materials to make strong load bearing ribs that experience significantly similar deflections on both light and hard kicking strokes.